The present invention relates to a process for removing finely divided potassium chloride from a water-soluble polar, aprotic solvent, which process involves the addition and removal of water to increase the particle size of the potassium chloride.
Potassium chloride is formed as a by-product in many chemical processes taking place in polar, aprotic solvents. Examples of such processes include the preparation of esters from acid chlorides and potassium salts of alcohols, phenols or pyridinols, the preparation of ethers by the reaction of aryl or alkyl chlorides with potassium salts of alcohols, phenols, or pyridinols, and the preparation of fluorinated compounds by treatment of chlorinated compounds with potassium fluoride When such reactions are carried out under essentially anhydrous or nearly anhydrous conditions, the potassium chloride that forms is finely divided and is difficult to remove from the solvent by sedimentation, filtration or centrifugation. Unacceptably incomplete removal and/or unacceptably long separation times are typical in such processes when removal by such means is attempted. Further, an unacceptably large amount of the solvent is typically lost in the separation due to entrainment. The separation of potassium chloride from polar, aprotic solvents is sometimes accomplished by distillation of the solvent from the mixture. This method is generally unsatisfactory because the salt that is separated remains in the distillation pot as a difficult-to-handle solid and is contaminated with the other non-volatile components of the mixture. It generally must be extensively purified before it can be recycled or used in other ways. Since polar, aprotic solvents are generally very soluble in water, it is not usually feasible to simply add sufficient water to dissolve the potassium chloride and then separate the aqueous solution from the solvent by decantation.
An improved process for removing finely divided potassium chloride from mixtures with dipolar, aprotic solvents is, accordingly, of considerable interest.